The main aim is to develop a protocol for enhancing the accuracy of image-based diagnostic systems in radiology and other medical fields such as cytology and clinical pathology. The protocol will be presented in a document intended for publication as a book in the open literature. The protocol will focus on the reduction of diagnostic error throught the reduction or variability in human judgements about health states as made by image readers and by clinicians whose diagnoses depend largely on reports about medical imagery. Analytical and experimental studies conducted to refine and illustrate the protocol will follow its four steps: (1) analyses of human factors in diagnostic accuracy to identify sources of substantial error and to determine possible remedies for such erros; (2) exploratory "in vitro" tests of promising techniques for reducing various kinds of sensory, perceptual, cognitive, and communicative errors; (3) quantitative performance studies of the intact conventional system and "in vivo" studies of error-reduction techniques; and (4) comparative analyses of accuracy and efficacy of various forms of the diagnostic system. These studies will be based on a suitable radiologic modality, and perhaps on additional modalities if such are desirable for comparison in particular respects. Errors-reduction techniques of interest include" (a) aids to acquisition of image data, perception of relevant image features, merging of image data into a reader's report, and communication between image reader and clinician; and also (b) the replication of readings within and across readers. The project depends directly on staff expertise in medical physics, experimental psychology, and quantitative modeling of behavior, and will employ an advisory panel that offers also broad research experience in radiology, nuclear medicine, statistics, and assessments of medical efficacy. Near-term objectives are acquanting the medical community with sytematic procedures for reducing variability in human diagnostic performance that go beyond standard procedures, and producing a practical guide for their immplementation. The long-term objective is significant, cost-effective enhancement of diagnostic accuracy over a wide range of diagnostic setting.